A. Field of the Invention
The invention relates to a dampening mechanism, particularly to a dampening mechanism utilizing viscous resistance.
B. Description of the Related Art
In a clutch disk assembly, generally, input portions (clutch plate, etc.) to which torque from the engine side is inputted and output portions (spline hub, etc.) which output torque to an output shaft are connected elastically in a circular direction by a torsion spring. The torsion spring is generally formed by a coil spring and can absorb torque fluctuations through expansion and contraction.
In order to absorb low load torque fluctuations, the twisting rigidity of a coil spring needs to be low. Generally, in order to have a low twisting rigidity for a coil spring, the wire diameter of the coil needs to be small. However, a coil with a small wire diameter reduces the capacity for torque transmission. Therefore, by making the diameter of a coil spring large, low rigidity is obtained without reducing torque transmission capacity. As a result, the volume occupied by the coil spring must be relatively large. The large size of the coil spring is an obstacle when it is necessary to reduce the dimensions of the clutch disc assembly.
To solve the problems described above, a dampening mechanism has been developed which includes elongated plate springs which have been bent into a wave or undulated shape. The elongated undulated spring extends in a circular direction within a fluid chamber of the dampening mechanism of the clutch disk assembly.
In the dampening mechanism, a plurality of fluid filled spaces are formed between plate springs, outer circumferential walls and side walls of the fluid chamber. When twisting vibrations are inputted in the dampening mechanism, the plate springs are compressed in a circular direction. At the same time, a plurality of fluid filled spaces contract and the fluid in the spaces flows outside. The fluid flows through a gap between the axially ending part of the plate springs and the side wall of the fluid chamber and generates a predetermined viscous resistance.
However, the above-mentioned viscous resistance generating mechanism does not always generate enough viscous resistance for excessive torque fluctuations during engagement or disengagement of the clutch.